1. Field of the Invention
The present invention relates to a diffractive optical element and a measuring device employing this diffractive optical element.
2. Description of the Related Art
Diffractive optical elements for diffracting at least a part of incident light are used in various kinds of optical devices, optical apparatuses, and the like. An optical three-dimensional measuring device serving as an example of such optical apparatuses projects a predetermined projection pattern of light onto a measurement object, then acquires an image of the measurement object onto which the predetermined projection pattern of light is projected, and thereby performs three-dimensional measurement. In such a three-dimensional measuring device, a diffractive optical element is used for generating such a predetermined projection pattern of light.
U.S. Pat. No. 6,101,269 and JP-A-2009-531655 disclose methods of projecting a speckle pattern generated by a diffractive optical element as a projection pattern of light to be projected onto the measurement object in three-dimensional measurement.
Nevertheless, in such a speckle pattern, light spots of strong intensity are generated at random positions on the projection plane. Thus, density inhomogeneity of light spots arises in the within-the-plane distribution on the projection plane. Thus, in a region onto which light spots in the speckle pattern are not projected, three-dimensional information is not acquired and hence accurate three-dimensional measurement is not achieved. This has caused a problem of degradation in the resolution of the three-dimensional measuring device.